A lot of times a dying PSU will still be able to spin things like fans and hard drives but not provide enough clean power to run the core components. The fact that the fans spin certainly doesn't mean the PSU is working correctly.
So I went back in and did some comprehensive RAM testing (using Memtest 86), and jotted down the results. Here are the results. Note that I have 2 RAM slots, which I'll call Slot 1 and Slot 2, and I'll call my Ram sticks "ramA" (the one that's already in Slot 1 before I started these Memtests) and "ramB" (the allegedly bad one I took out at the end of my previous post).
Test 1: Removed both sticks, then put ramB in slot 1.
Results: No errors. Odd, so it seems the allegedly bad ram isn't bad after all.
Test 2: Remove, then put ramA in slot 1.
Results: No errors. OK, so both sticks seem to be good by themselves.
Test 3: Put ramA in slot1 and ramB in slot2.
Results: Memtest froze midway! Then when I force a reboot, there's no signal to LCD again!
Test4: Switch them up. ramB in slot1 and ramA in slot2
Results: LCD works again, boot to memtest ok, but froze at 62%. When I reboot after the freeze, again no signal monitor.
Notes so far: So it seems that both of sticks together is causing the problem, and very consistently! My next test will be to test to see if my DIMM slot2 itself is the culprit.
Test5: Remove both sticks. Put ramB in slot 2
Results: Memtest ran. Errors reported at around 20% of test! (ECC correctable error). And then it reboots itself then the test is about 60% done. But when it reboots, no signal to monitor again.
Test6: Remove stick. Put ramA in slot 2
Result: Memtest ran, then suddenly screen goes crazy with colors midway. need to reboot again.
In the end, I went back to working with one stick of ram (RamB in Slot1), and I'll run my system like this for a while to see if anything develops. But my system ~seems~ to work fine so far, but with 1/2 the RAM.
So all in all, it seems the DIMM slot 2 itself is the culprit! (ie mobo is bad). Is this a fair conclusion? Can anyone think of anything else?